Resin composition and multilayer structure including the same

ABSTRACT

The present invention provides a resin composition comprising a saponified ethylene-vinyl acetate copolymer (A) and a substituted 9,10-anthraquinone (B) having a substituent at at least one of the 2-, 3-, 6- and 7-positions and showing a percent weight loss when stood with heating at 250° C. for 60 minutes of not more than 5% and a multilayer structure including the resin composition as an intermediate layer. This multilayer structure is superior in appearance, oxygen barrier property, further forming stability, resistance to pinholes, adhesion between layers and the like, and is useful for packaging of foods such as meat, ketchup, soybean paste, beer and the like.

TECHNICAL FIELD

The present invention relates to a saponified ethylene-vinyl acetatecopolymer (hereinafter to be abbreviated as EVOH) composition and amultilayer structure thereof. More particularly, the present inventionrelates to an EVOH composition useful for obtaining a laminate structuresuperior in oxygen barrier property and appearance, particularly formingstability upon processing at high temperature, and further, adhesionbetween layers and a multilayer structure using the composition.

BACKGROUND ART

In general, EVOH is a resin superior in gas barrier property,transparency, melt formability and the like, and is known to suppressdeterioration of food when used as a material for packaging food, byfunctionally blocking oxygen.

Improved oxygen barrier property has been desired in recent years toincrease safety of food. In addition, the food highly sensitive tooxygen, which has been preserved in metal and glass bottles, also tendsto be preserved in plastic containers due to ease of use. In this case,too, higher oxygen barrier property is requested.

On the other hand, since not only external oxygen but also oxygenremaining inside by being enclosed with a packaging material used forpackaging the food have a possibility of deteriorating the food, removalof such oxygen has been desired.

From such background, a resin composition capable of physically blockingthe external oxygen and absorbing internal oxygen as well has beenconsidered.

For example, JP-A-8-238726 describes a laminate having at least twolayers of a layer for physically blocking the oxygen and a layer forchemically absorbing the oxygen, wherein the layer for chemicallyabsorbing the oxygen is an alloy mainly comprising aluminum;JP-A-11-151783 describes a laminate comprising an oxygen barrier layerand an oxygen absorptive layer as intermediate layers, wherein theoxygen absorptive layer comprises a composition of a thermoplasticresin, a reduced iron and a halogenated metal, JP-T-8-504851 describes alaminate comprising, as an intermediate layer, a composition comprisingan anthraquinone compound and a polymer, JP-T-11-504666 describes oxygencapture material comprising an anthraquinone compound in an oxygenimpermeable section or microcapsule, JP-A-3-197566 describes a laminatestructure comprising a composition wherein polyhydric phenol and anelectron donating substance are added to EVOH as an intermediate layer,JP-T-8-502202 describes a laminate structure comprising a compositionwherein a cobalt catalyst and a photoinitiator are added to a polymerhaving an unsaturated hydrocarbon bond, U.S. Pat. No. 6,037,022describes a food container comprising a laminate comprising acomposition wherein iron carbonate is added to EVOH and JP-A-2-298579describes a laminate comprising a composition wherein reduced iron isadded to EVOH.

The present applicant has made further improvements in the respectivetechniques disclosed above and a multilayer structure having a layer ofa resin composition comprising EVOH and a substituted 9,10-anthraquinonehaving a substituent at at least one of the 2-, 3-, 6- and 7-positions(Japanese Patent Application No. 2001-299898).

When the above-mentioned multilayer structure that the resent applicantproposed is produced in a general melt-forming temperature range ofabout 220° C., a multilayer structure superior in formability, adhesionbetween layers, resistance to pinholes, resistance to delamination andthe like can be obtained, but a resin composition having fine high speedformability has been recently desired from the market, which sometimesresults in forming at a relatively high temperature of about 250° C.rather than the conventional forming temperature of about 220° C. Whenformed at such temperature, the forming stability is degraded and theadhesion between layers shows a slight decrease, thus leaving room forimprovement.

DISCLOSURE OF THE INVENTION

The present inventors have conducted intensive studies in view of theabove-mentioned situation and found that a resin composition comprisingEVOH (A) and substituted 9,10-anthraquinone (B) having a substituent atat least one of the 2-, 3-, 6- and 7-positions and showing a percentweight loss when stood with heating at 250° C. for 60 minutes of notmore than 5% meets the above-mentioned object, which resulted in thecompletion of the present invention.

When producing a resin composition containing the above-mentioned (A)and (B) in the present invention, moreover, a substituted9,10-anthraquinone (B) having a substituent at at least one of the 2-,3-, 6- and 7-positions and showing a percent weight loss when stood withheating at 250° C. for 60 minutes of not more than 5% is melt-mixed withEVOH (A) having a water content of not more than 60 wt % (preferably20-60 wt %) in an extruder, whereby the action and effect of the presentinvention is remarkably exhibited.

In the present invention, moreover, addition of 0.001-0.5 equivalent ofacid (C) to a substituted 9,10-anthraquinone (B) having a substituent atat least one of the 2-, 3-, 6- and 7-positions and showing a percentweight loss when stood with heating at 250° C. for 60 minutes of notmore than 5% further exhibits the effect of the present invention.

In a specific layer constitution of a multilayer structure using theresin composition of the present invention, the resin composition layeris preferably an intermediate layer, and at least one layer of the innerand outer layers is preferably a layer containing a resin selected froma polyolefin resin, a polyamide resin and a polyester resin.

Accordingly, the present invention provides the following.

(1) A resin composition comprising a saponified ethylene-vinyl acetatecopolymer (A) and a substituted 9,10-anthraquinone (B) having asubstituent at at least one of the 2-, 3-, 6- and 7-positions andshowing a percent weight loss when stood with heating at 250° C. for 60minutes of not more than 5%.

(2) The resin composition of the above-mentioned (1), wherein thesubstituted 9,10-anthraquinone (B) having a substituent at at least oneof the 2-, 3-, 6- and 7-positions and showing a percent weight loss whenstood with heating at 250° C. for 60 minutes of not more than 5% iswater-soluble.

(3) The resin composition of the above-mentioned (1) or (2), whereinsubstituted 9,10-anthraquinone (B) having a substituent at at least oneof the 2-, 3-, 6- and 7-positions and showing a percent weight loss whenstood with heating at 250° C. for 60 minutes of not more than 5% issodium anthraquinone-sulfonate or disodium anthraquinone-disulfonate.

(4) The resin composition of any of the above-mentioned (1)-(3), whereinthe content of the substituted 9,10-anthraquinone (B) having asubstituent at at least one of the 2-, 3-, 6- and 7-positions andshowing a percent weight loss when stood with heating at 250° C. for 60minutes of not more than 5% is 0.5-10 wt % relative to the saponifiedethylene-vinyl acetate copolymer (A).

(5) The resin composition of any of the above-mentioned (1)-(4), furthercomprising an acid (C) in 0.001-0.5 equivalent of the substituted9,10-anthraquinone (B) having a substituent at at least one of the 2-,3-, 6- and 7-positions and showing a percent weight loss when stood withheating at 250° C. for 60 minutes of not more than 5%.

(6) The resin composition of any of the above-mentioned (1)-(5), whichis obtained by melt-mixing a saponified ethylene-vinyl acetate copolymer(A) having a water content of not more than 60 wt % and a substituted9,10-anthraquinone (B) having a substituent at at least one of the 2-,3-, 6- and 7-positions and showing a percent weight loss when stood withheating at 250° C. for 60 minutes of not more than 5% in an extruder.

(7) A laminate structure comprising a layer made of the resincomposition of any of the above-mentioned (1)-(6) as an intermediatelayer, and at least one layer of inner and outer layers comprises aresin selected from a polyolefin resin, a polyamide resin and apolyester resin.

(8) The laminate structure of the above-mentioned (7), wherein the innerand outer layers comprises a polyolefin resin.

(9) The resin composition of the above-mentioned (6), wherein thesaponified ethylene-vinyl acetate copolymer (A) has a water content of20-60 wt %.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is described in detail in the following.

While the EVOH (A) to be used in the present invention is notparticularly limited, the ethylene content is preferably 5-50 mol %(further 10-50 mol %, particularly 20-50 mol %, especially 25-50 mol %).When the ethylene content is less than 5 mol %, the water resistancebecomes insufficient and when it exceeds 50 mol %, the gas barrierproperty is unpreferably degraded.

The saponification degree of the vinyl acetate component is preferablynot less than 90 mol % (further not less than 95 mol %, particularly notless than 99 mol %, especially not less than 99.5 mol %). When thesaponification degree is less than 90 mol %, the gas barrier propertyand heat resistance unpreferably becomes insufficient.

Furthermore, the melt flow rate (MFR) (210° C., load: 2160 g) ispreferably 0.1-50 g/10 min (further 1-30 g/10 min, particularly 2-20g/10 min, especially 5-15 g/10 min). When the MFR is less than 0.1 g/10min, the resin pressure becomes high during melt-forming, making theforming difficult, and when it conversely exceeds 50 g/10 min, theresulting formed product unpreferably shows decreased resistance topinholes.

The above-mentioned EVOH (A) may comprise a copolymerizableethylenically unsaturated monomer copolymerized therein, as long as theobject of the present invention is not impaired. As such monomer,olefins such as propylene, 1-butene, isobutene and the like, unsaturatedacids such as acrylic acid, methacrylic acid, crotonic acid, phthalicacid (phthalic anhydride), maleic acid (maleic anhydride), itaconic acid(itaconic anhydride) and the like or a salt thereof or mono- or di-alkylester thereof having 1 to 18 carbon atoms, acrylamides such asacrylamide, N-alkylacrylamide having 1 to 18 carbon atoms,N,N-dimethylacrylamide, 2-acrylamidepropanesulfonic acid or a saltthereof, acrylamidepropyldimethylamine or an acid salt thereof or aquaternary salt thereof and the like, methacrylamides such asmethacrylamide, N-alkylmethacrylamide having 1 to 18 carbon atoms,N,N-dimethyl methacrylamide, 2-methacrylamidepropanesulfonic acid or asalt thereof, methacrylamidepropyldimethylamine or an acid salt thereofor a quaternary salt thereof and the like, N-vinylamides such asN-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide and the like,cyanated vinyls such as acrylonitrile, methacrylonitrile and the like,vinyl ethers such as alkylvinyl ether having 1 to 18 carbon atoms,hydroxyalkylvinyl ether, alkoxyalkylvinyl ether and the like,halogenated vinyls such as vinyl chloride, vinylidene chloride, vinylfluoride, vinylidene fluoride, vinyl bromide and the like, allylacetate, allyl chloride, allyl alcohol, dimethylallyl alcohol,trimethyl-(3-acrylamide-3-dimethylpropyl)-ammonium chloride,acrylamide-2-methylpropanesulfonic acid and the like can be mentioned.In addition, post-modification such as urethanation, acetalation,cyanoethylation and the like-may be applied without departing from thescope of the present invention. As EVOH (A), moreover, for example,silicon-containing EVOH described in JP-A-60-144304 may be also used.

The substituted 9,10-anthraquinone (B) having a substituent at at leastone of the 2-, 3-, 6- and 7-positions and showing a percent weight losswhen stood with heating at 250° C. for 60 minutes of not more than 5%(hereinafter sometimes to be simply referred to as anthraquinone (B)) tobe used in the present invention needs to show a percent weight losswhen stood with heating at 250° C. for 60 minutes of not more than 5%(further not more than 4%, particularly not more than 3%). When thepercent weight loss when stood with heating exceeds 5%, the formingstability at 250° C. decreases, thus making achievement of the object ofthe present invention difficult.

The percent weight loss by heating can be determined, for example, usingthermobalance TGA from the weight loss when left standing at 250° C. for60 minutes. To be more precise, it can be determined using“thermobalance TGA TG8120” manufactured by Perkin Elmer, Inc. and thelike. For the measurement of the percent weight loss by heating,anthraquinone (B) needs to be sufficiently dried before measurement, andwater contained as crystal water also needs to be removed. When there isscarcely a vaporization component at a low temperature other than water,anthraquinone is left standing at 100-1200C for about 10-60 min in TGAmeasurement until the weight loss ceases, and then the temperature israised to 250° C. to measure the weight loss. When there are manyvaporization components at a low temperature, water in the vaporizationcomponents can be measured by a method comprising passing vaporizationcomponents generated in TGA measurement through a tube packed withcalcium carbonate and confirming changes in the weight, or by sealinganthraquinone in an ampoule, retaining at 250° C. and analyzingcomponents of the gas in the ampoule by gas chromatography-massspectrometry (GC-MS). However, when there are many vaporizationcomponents other than water at 100-120° C., the number of suchcomponents tends to increase at 250° C. and the weight change generallyfar exceeds 5%.

In addition, anthraquinone (B) is also required to have a substituent atat least one of the 2-, 3-, 6- and 7-positions, and the substituent isnot particularly limited and, for example, nitro group, sulfonaminogroup, sulfonate group and the like can be mentioned. Preferably,anthraquinone (B) having a sulfonate group as a substituent is used andfor imparting the water-solubility to be mentioned later, sodiumsulfonate is particularly preferable.

Of the above-mentioned anthraquinone (B), water-soluble ones arepreferable in consideration of the compatibility with EVOH (A). By beingwater-soluble is meant solubility in water at 25° C. of not less than0.1%.

The resin composition of the present invention contains theabove-mentioned EVOH (A) and anthraquinone (B), and the content(addition) ratio thereof is not particularly limited. However,anthraquinone (B) is preferably contained in a proportion of 0.5-10 wt %relative to EVOH (A). When the content is less than 0.5 wt %, oxygenpermeability increases possibly because the oxygen absorbability isdegraded, and when it conversely exceeds 10 wt %, appearance is degradedand oxygen permeability again unpreferably increases possibly becausegas barrier property of EVOH decreases. More preferable lower limit ofthe content is 1 wt %, more preferable upper limit is 8 wt % and isparticularly 6 wt %.

Production of the above-mentioned resin composition is not particularlylimited, and EVOH (A) and anthraquinone (B) only need to be mixed. Inthis case, use of EVOH having a water content of not more than 60 wt %(further 20-60 wt %, particularly 25-50 wt %, especially 25-40 wt %) asEVOH (A) is preferable because generation of a foreign substance when afilm is formed is suppressed. When the water content exceeds 60 wt %,the amount of foreign substance unpreferably tends to increase possiblybecause water containing anthraquinone (B) is easily discharged fromEVOH (A) when a film is formed.

How to obtain such water-containing EVOH (A) is not particularlylimited. In general, an EVOH solution is extruded in strands into acoagulation liquid to allow coagulation thereof, which is followed bycutting to give pellets and a treatment by washing with water. The watercontent of EVOH can be controlled during these steps.

For the measurement of the above-mentioned water content, EVOH isweighed with an electronic balance {W1 (g)}, placed in a hot air ovendryer maintained at 150° C., dried for 5 hr, allowed to cool in adesiccator for 30 min, weighed {W2 (g)) and calculated by the followingformula.Water content (%)={(W1−W2)/W1}×100

For mixing EVOH (A) and anthraquinone (B) in the present invention,industrially, EVOH (A) and anthraquinone (B) are preferably suppliedinto a single screw or a twin screw melt extruder, and melt-mixed in theextruder to give a resin composition. Particularly, the use of a twinscrew extruder is preferable because EVOH (A) and anthraquinone (B) aremixed well. In addition, the residence time of the resin composition inthe extruder is not less than 20 seconds and desirably within 20minutes.

Generally, the above-mentioned melt-mixed resin composition is extrudedin strands, cut into pellets, dried as necessary in a dryer and thelike, or, after reducing the water content by removing water from thebent part of the extruder with a vacuum pump and the like, extruded instrands and cut into pellets.

In this way, the resin composition of the present invention is obtained.In the present invention, for improving the forming stability at hightemperatures, 0.001-0.5 equivalent (further 0.005-0.2 equivalent,particularly 0.01-0.1 equivalent) of an acid (C) relative toanthraquinone (B) is preferably added. The acid (C) is not particularlylimited but organic acids such as acetic acid, propionic acid, butyricacid, lauric acid, stearic acid, oleic acid, behenic acid, adipic acid,benzoic acid, citric acid, nicotinic acid and the like, inorganic acidssuch as hydrochloric acid, sulfuric acid, sulfurous acid, carbonic acid,phosphoric acid, boric acid and the like can be mentioned. To impartforming stability for a long time, citric acid and nicotinic acid arepreferable from those mentioned above.

The resin composition of the present invention may contain, in additionto the above-mentioned (A)-(C), alkali metal salts (sodium, potassiumetc.) with acids (acetic acid, boric acid, phosphoric acid etc.), metalsalts of alkaline earth metal, transition metal and the like, lubricantssuch as saturated aliphatic amide (e.g., stearic acid amide etc.),unsaturated fatty acid amide (e.g., oleic acid amide etc.), bisfattyacid amide (e.g., ethylenebisstearic acid amide etc.), fatty acid metalsalt (excluding magnesium salt, calcium salt, zinc salt), low molecularweight polyolefin (e.g., low molecular weight polyethylene withmolecular weight of about 500-10,000, low molecular weight polypropyleneetc.) and the like, inorganic salts (e.g., hydrotalcite etc.),plasticizers (e.g., aliphatic polyhydric alcohols such as ethyleneglycol, glycerine, hexanediol and the like, and the like), antioxidants,UV absorbers, crystal nucleating agents, coloring agents, antistaticagents, surfactants, desiccants, antibacterial agents, antiblockingagents (e.g., talc fine particles etc.), slipping agents (e.g.,amorphous silica etc.), fillers (e.g., inorganic filler etc.), otherresins (e.g., polyolefin resin, polyester resin, polyamide resin,polystyrene resin, polyvinyl chloride resin, polyvinylidene chloride,acrylic resin, vinylester resin, polyester elastomer, polyurethaneelastomer, chlorinated polyethylene, chlorinated polypropylene, aromaticand aliphatic polyketone, aliphatic polyalcohol etc.) and the like,within the range not departing from the object of the present invention.However, the amount thereof does not exceed the weight of thecomposition. In addition, other EVOHs (EVOH having different ethylenecontent, saponification degree, MFR and the like) and the like may beadded.

The resin composition of the present invention is useful for amultilayer structure. Such multilayer structure is explained in thefollowing.

Such multilayer structure comprises at least one layer made from theabove-mentioned resin composition and for the production of themultilayer structure, other substrate only needs to be laminated on oneor both surfaces of the layer made from the resin composition. As thelamination method, for example, a method comprising melt extrusion of athermoplastic resin on a film or sheet made from the resin composition,a method conversely comprising melt extrusion of the resin compositionon the substrate made from a thermoplastic resin and the like, a methodcomprising co-extrusion of the resin composition and other thermoplasticresin, further, a method comprising dry laminating a film or sheet madefrom the resin composition and a substrate film or sheet using knownadhesives such as an organic titanium compound, an isocyanate compound,a polyester compound, a polyurethane compound and the like and the likecan be mentioned.

As the above-mentioned thermoplastic resin, polyolefin resin, polyesterresin, polyamide resin, polystyrene resin, polyvinyl chloride resin,polyvinylidene chloride, acrylic resin, vinylester resin, polyesterelastomer, polyurethane elastomer, chlorinated polyethylene, chlorinatedpolypropylene, aromatic and aliphatic polyketone, aliphatic polyalcoholand the like can be mentioned, and polyolefin resin, polyester resin andpolyamide resin are preferably used. Of these, polyolefin resin ispreferably used for the application to containers such as bottle and thelike.

As such polyolefin resin, a wide range of polyolefin resins includinghomo or copolymers of olefins such as linear low density polyethylene(LLDPE), low density polyethylene (LDPE), very low density polyethylene(VLDPE), moderate density polyethylene (MDPE), high density polyethylene(HDPE), ethylene-vinyl acetate copolymer (EVA), ionomer,ethylene-propylene (block or random) copolymer, ethylene-acrylic acidcopolymer, ethylene-acrylate copolymer, ethylene-methacrylic acidcopolymer, ethylene-methacrylate copolymer, polypropylene,propylene-α-olefin (α-olefin having 4 to 20 carbon atoms) copolymer,polybutene, polypentene, polymethylpentene and the like, homo orcopolymers of these olefins graft modified with unsaturated carboxylicacid or an ester thereof, blends of these and the like can be mentioned.Particularly, linear low density polyethylene (LLDPE), low densitypolyethylene (LDPE), very low density polyethylene (VLDPE),ethylene-vinylacetate copolymer (EVA) and ionomer are preferable in thatthey are superior in the bending fatigue resistance, vibration fatigueresistance and the like of the obtained laminate packaging material.

Particularly, linear low density polyethylene comprising anethylene-α-olefin copolymer having a density of 0.86-0.95 g/cm³ ispreferably used. When the density is smaller than the above-mentionedrange, various mechanical properties of the laminate packaging materialmay be insufficient, or blocking may occur. Conversely when it islarger, the bending fatigue resistance, vibration fatigue resistance andthe like may unpreferably become insufficient. As used herein, thedensity is measured at 20° C. according to JIS K6760, and theethylene-α-olefin copolymer is a copolymer of ethylene and α-olefinhaving not more than 18 carbon atoms such as butene-1, pentene-1,4-methylpentene-1, hexene-1, octene-1 and the like. Of these, anethylene-α-olefin copolymer comprising α-olefin having 4 to 8 carbonatoms is preferably used.

The above-mentioned linear low density polyethylene is preferably anethylene-α-olefin copolymer produced in the presence of a single sitecatalyst because the effect of the present invention can be expressedfully. A single site catalyst is a catalyst characterized in that theactive site is uniform (single site), while the existing Zieglercatalyst and Phillips catalyst have non-uniform active sites and arereferred to as multi-site catalysts, and representative single sitecatalyst includes metallocene catalyst and the like. As a specificproduct name, Kernel (Japan Polychem Corporation), Evolue (MitsuiChemicals), Exact (Exxon Chemical Company), Affinity (The Dow ChemicalCompany) and the like can be mentioned.

As such polyamide resin, polycapramide (nylon 6), poly-ω-aminoheptanoicacid (nylon 7), poly-ω-aminononanoic acid (nylon 9), polyundecaneamide(nylon 11), polylauryl lactam (nylon 12), polyethylenediamine adipamide(nylon 26), polytetramethylene adipamide (nylon 46), polyhexamethyleneadipamide (nylon 66), polyhexamethylene sebacamide (nylon 610),polyhexamethylene dodecamide (nylon 612), polyoctamethylene adipamide(nylon 86), polydecamethylene adipamide (nylon 108), caprolactam/lauryllactam copolymer (nylon 6/12), caprolactam/ω-aminononanoic acidcopolymer (nylon 6/9), caprolactam/hexamethylenediammonium adipatecopolymer (nylon 6/66), lauryl lactam/hexamethylenediammonium adipatecopolymer (nylon 12/66), ethylenediamineadipamide/hexamethylenediammonium adipate copolymer (nylon 26/66),caprolactam/hexamethylenediammonium adipate/hexamethylenediammoniumsebacate copolymer (nylon 66/610), ethyleneammoniumadipate/hexamethylenediammonium adipate/hexamethylenediammonium sebacatecopolymer (nylon 6/66/610), polyhexamethylene isophthalamide,polyhexamethylene terephthalamide, hexamethyleneisophthalamide/terephthalamide copolymer or these polyamide resinsdenatured with aromatic amines such as methylenebenzylamine,m-xylenediamine and the like, m-xylylenediammonium adipate and the likecan be mentioned and in the present invention, one kind thereof or ablend of two or more kinds thereof can be used.

In addition, one wherein the carboxyl group and/or amino group on themolecule terminal of polyamide resin is adjusted (denatured) withalkylmonocarboxylic acid, alkyldicarboxylic acid, alkylmonoamine,alkyldiamine and the like can be also used.

As such polyester resin, condensation polymers comprising aromaticdicarboxylic acid or these alkyl esters and glycol as main componentscan be specifically mentioned, and the representative one preferablycomprises ethyleneterephthalate as a major repeating unit. Moreover, itis possible to contain a copolymerizable component as long as theprocessability, strength and the like are not drastically impaired. Assuch copolymerizable component, aromatic dicarboxylic acids such asisophthalic acid, diphenyl-4,4′-dicarboxylic acid,diphenoxyethanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid,2,7-naphthalenedicarboxylic acid and the like and ester formingderivatives of these, aliphatic dicarboxylic acids such as adipic acid,sebacic acid, azelaic acid, succinic acid and the like, and esterforming derivatives of these, alicyclic dicarboxylic acids such ascyclohexanedicarboxylic acid, hexahydroterephthalic acid and the likeand ester forming derivative of these, oxy acids such as p-oxybenzoicacid, oxycaproic acid and the like and ester forming derivatives ofthese, trimellitic acid, pyromellitic acid and the like can be mentionedfor an acid component.

As the glycol component, aliphatic glycols such as diethylene glycol,trimethylene glycol, tetramethylene glycol, neopentyl glycol and thelike, alicyclic glycols such as 1,4-cyclohexanedimethanol and the like,aromatic glycols such as bisphenol A, alkyleneoxide adduct of bisphenolA and the like, polyalkylene glycols such as polyethylene glycol,polypropylene glycol, polytetramethylene glycol and the like, glycerine,1,3-propanediol, pentaerythritol and the like can be mentioned.

The ethyleneterephthalate unit content is about 75-100 mol %, preferably85-100 mol %. Preferable intrinsic viscosity (measured in a 50 wt %/50wt % mixed solvent of phenol and tetrachloroethane at 30° C.) is 0.5-1.3dl/g (further 0.65-1.2 dl/g).

As a representative example, one comprising ethyleneterenaphthalate as amajor repeating unit can be mentioned. It is possible to add acopolymerizable component similar to the above, and theethyleneterenaphthalate content is about 75-100 mol %, preferably 85-98mol %. Preferable intrinsic viscosity is 0.4-1.2 dl/g (further 0.55-1.0dl/g).

In addition, use of a blend of the above-mentioned ethyleneterephthalatepolyester resin and an ethyleneterenaphthalate resin is preferable inthat the gas barrier property, UV blocking property and melt formabilityincrease. In this case, the blending ratio is 5-90 wt %, further 15-85wt %, of ethyleneterephthalate polyester resin, and 95-10 wt %, further85-15 wt %, of ethyleneterenaphthalate polyester resin.

Furthermore, as long as various properties are not markedly impaired,other thermoplastic resins and additives can be added, and as thethermoplastic resin, MXD-6 nylon, polycarbonate, polyallylate, liquidcrystalline polymer and the like can be mentioned.

When a formed product such as a film, a sheet and the like is onceobtained from the above-mentioned resin composition, which is thenextrusion-coated with other substrate or laminated with other filmsubstrate, sheet substrate and the like using an adhesive, as long asthe object of the present invention is not deviated, any substrate(paper, metal foil, non-oriented, monoaxially oriented or biaxiallyoriented plastic film or sheet and an inorganic material vapor depositedproduct thereof, woven fabric, non-woven fabric, metal cotton, woodetc.) can be used besides the above-mentioned thermoplastic resins.

The layer constitution of the multilayer structure of the presentinvention is not only a two layer structure of a/b, but any combinationsuch as b/a/b, a/b/a, al/a2/b, a/b1/b2, b2/b1/a/b1/b2, b1/b2/a/b3/b4,a1/b1/a2/b2 and the like can be employed as long as it is a film, asheet or a bottle, wherein the layer made from a resin composition is a(a1, a2, . . . ) and other substrate, such as a thermoplastic resinlayer is b (b1, b2, . . . ), with particular preference given to a layerconstitution of b/a/b or b2/b1/a/b1/b2. In the case of a filament, anycombination is possible, wherein a and b are bimetals, core (a)-sheath(b), core (b)-sheath (a), eccentric core-in-sheath type and the like.

In the above-mentioned layer constitution, an adhesive resin layer canbe formed between the respective layers as necessary. As such adhesiveresin, various ones can be used. While subject to change depending onthe kind of resin b, a modified olefin polymer having a carboxyl group,which is obtained by chemically bonding unsaturated carboxylic acid oran anhydride thereof to an olefin polymer (the aforementioned wide rangeof polyolefin resins) by addition reaction, grafting reaction and thelike can be mentioned. Specifically, one kind or a mixture of two ormore kinds selected from maleic anhydride grafted polyethylene, maleicanhydride grafted polypropylene, maleic anhydride graftedethylene-propylene (block or random) copolymer, maleic anhydride graftedethylene-ethylacrylate copolymer, maleic anhydride graftedethylene-vinylacetate copolymer and the like can be mentioned as apreferable one. The amount of the unsaturated carboxylic acid or ananhydride thereof to be contained in a olefin polymer here is preferably0.001-3 wt %, more preferably 0.01-1 wt %, particularly preferably0.03-0.5 wt %. When the amount of modification in a modified product issmall, adhesive property may become insufficient, and when it isconversely large, crosslinking reaction sometimes occurs to unpreferablydegrade the formability. These adhesive resins may be blended with arubber-elastomer component such as resin composition, other EVOH,polyisobutylene, ethylene-propylene rubber and the like, further a resinof layer b and the like. Particularly, by blending with a polyolefinresin different from the polyolefin resin, which is the matrix of theadhesive resin, the adhesiveness may be usefully improved.

A specific mode of the most preferable laminate structure of theabove-mentioned multilayer structure in the case of a bottle is apolyethylene layer/adhesive resin layer/layer of resincomposition/adhesive resin layer/polyethylene layer, polypropylenelayer/adhesive resin layer/layer of resin composition/adhesive resinlayer/polypropylene layer, polyester resin layer/layer of resincomposition/polyester resin layer or polyester resin layer/layer ofresin composition/polyester resin layer/layer of resincomposition/polyester resin layer and the like can be mentioned, whichcomprises polyolefin resin or polyester resin in inner and outer layers.In the case of a film, polyethylene resin layer /adhesive resinlayer/layer of resin composition/adhesive resin layer/polyethylene resinlayer, polyethylene resin layer/adhesive resin layer/polyamideresin/layer of resin composition/adhesive resin layer/polyethylene resinlayer, polyamide resin layer/layer of resin composition/polyamide resinlayer, polyethylene resin layer/adhesive resin layer/polyamide resinlayer/layer of resin composition /polyamide resin layer and the like canbe mentioned.

The thickness of each layer of the multilayer structure varies dependingon the layer constitution, the kind of b, use, form of container,required properties and the like. In general, the thickness of layer ais 5-500 μm (further 10-200 μm), that of layer b is 5-5000 μm (further30-1000 μm), and that of adhesive resin layer is about 5-400 μm (further10-150 μm). When layer a is less than 5 μm thick, gas barrier propertybecomes insufficient and control of the thickness is unstable, and whenit conversely exceeds 500 μm, the bending fatigue resistance becomesinferior, the film unpreferably becomes uneconomical, and when layer bis less than 5 μm thick, the rigidity becomes insufficient, and when itconversely exceeds 5000 μm, the bending fatigue resistance becomesinferior, and the weight becomes unpreferably large. When the adhesiveresin layer is less than 5 μm thick, adhesion between layers becomesinsufficient, and the control of the thickness becomes unstable, andwhen it conversely exceeds 400 μm, the weight becomes larger and thefilm unpreferably becomes uneconomical.

In addition, the aforementioned various additives and modifiers,fillers, other resin and the like can be also added to improve formingprocessing property and various properties of each layer of themultilayer structure of the present invention, within the range thatdoes not inhibit the effect of the present invention.

The multilayer structure is used as it is for various shapes. To improveproperties of the multilayer structure, a stretch treatment ispreferably applied. For such stretching, monoaxial stretching or biaxialstretching may be employed, wherein drawing at the highest ratioproduces formed products such as stretch film, stretch sheet, stretchcontainer, stretch bottle and the like, which are superior in propertiesand free from pinholes, cracks, inconsistent stretching, delaminationand the like during stretching.

As the stretching method, roll stretching, tenter stretching, tubularstretching, stretch blowing and the like, as well as deep draw forming,vacuum pneumatic forming and the like having high draw ratio can beemployed. For biaxial stretching, both simultaneous biaxial stretchingmethod and sequential biaxial stretching method can be employed. Thetemperature for stretching is about 60-170° C., preferably 80-160° C.

After stretching is completed, heat setting is preferably performedsequentially. Heat setting can be performed by a known means, byheat-treating the above-mentioned stretched film at 80-170° C.,preferably 100-160° C., for about 2-600 seconds while maintaining thefilm under tension.

When, for example, a cup or tray like multilayer container is to beobtained from a multilayer sheet or a multilayer film, draw formingmethod is employed. Specifically, vacuum forming method, pneumaticforming method, vacuum pneumatic forming method, plug assisting vacuumpneumatic forming method and the like can be mentioned.

When a tube or bottle like multilayer container is obtained from amultilayer parison (hollow tube-like preliminarily formed product beforeblowing), blow forming method is employed. Specifically, extrusion blowforming (twin-head, double station type, parison shift, rotary,accumulator, horizontal parison etc.), cold parison blow forming,injection blow forming, biaxial stretch blow forming (extrusion coldparison biaxial stretch blow forming, injection cold parison biaxialstretch blow forming, injection forming inline biaxial stretch blowforming etc.) and the like can be mentioned.

When a multilayer container is to be produced, a multilayer containercan be also directly obtained using a coinjection forming machine andthe like.

The thus-obtained multilayer structure may have any form such as film,sheet, tape, bottle, pipe, filament, modified cross-section extrudateand the like. In addition, the obtained multilayer structure can beapplied to heat treatment, cooling treatment, rolling treatment,printing treatment, dry laminate treatment, solution or melt-coatingtreatment, bag making processing, deep drawing processing, boxingprocessing, tube processing, split processing and the like as necessary.

The containers such as cup, tray, tube, bottle and the like, bags andlids made of a stretched film, which are obtained as mentioned above areuseful as various containers for general foods, seasoning such asmayonnaise, dressing and the like, fermented food such as soybean pasteand the like, oil and fat food such as salad oil and the like, beveragessuch as juice, carbonated beverage, beer, wine and the like, cosmetic,pharmaceutical products, detergent, flagrance cosmetic, industrialdrugs, agricultural chemicals, fuel and the like. The multilayerstructure of the present invention is particularly useful for containersof liquid food (including drink products) and the like. In addition, themultilayer structure of the present invention can be preferably used forpackaging material for boil treatment and retort treatment.

In this way, the multilayer structure of the present invention superiorin gas (oxygen) barrier property, forming stability, and further in theresistance to delamination and resistance to pinholes can be obtained.To fully express the oxygen barrier property, particularly oxygencapture ability, of the multilayer structure, the resin composition inthe multilayer structure is preferably exposed to ultraviolet ray (UV)or electron beam (EB). In view of the cost of the device and runningcost, use of UV irradiation is preferable. While the method of UVirradiation is not particularly limited, UV from a UV generation sourcesuch as high pressure mercury lamp, ultra-high pressure mercury lamp,carbon arc lamp, xenon lamp, metal halide lamp, chemical lamp and thelike can be irradiated to the laminate structure. When the layer of theresin composition is not disposed on the surface, a highly transparentlayer may be formed on the surface layer, so as to let the UV passthrough to the layer of resin composition.

The irradiation amount of UV varies depending on the amount of component(B) in the resin composition, use of the laminate structure and thelike, UV irradiation at about 200-5000 mJ/cm² (further 500-5000 mJ/cm²)is sufficient.

EXAMPLES

The present invention is explained in detail by referring to Examples,which are not to be construed as limitative.

In the Examples “parts” and “%” are based on weight unless otherwisespecified.

Example 1

EVOH (A) [ethylene content 32 mol %, saponification degree 99.5 mol %,MFR-12 g/10 min (210° C., load: 2160 g)] having a water content of 35%and 9,10-anthraquinone-β-sodium sulfonate (B) [percent weight loss byheating at 250° C. for 60 min of 0.1%] were supplied to a twin screwextruder (30 mmφ, L/D=42, molten temperature 95° C.) such that theamount of 9,10-anthraquinone-β-sodium sulfonate (B) added was 3%relative to EVOH (A) without water and melt-mixed therein. The moltenmixture was extruded in strands on a belt, cooled and cut with apelletizer to give pellets of a resin composition containing theabove-mentioned (A) and (B). These pellets were dried overnight in avacuum drying machine at 90° C. and further dried at 140° C. for 4 hr ina fluidized dryer under a nitrogen stream.

Using the obtained resin composition (pellet) and according to thefollowing, a multilayer structure was formed and subjected toevaluation.

[Production of Multilayer Structure-Multilayer Film]

The obtained resin composition (pellet), polyethylene [high densitypolyethylene, Novatec HD HB431 manufactured by Japan PolychemCorporation, MFR 0.35 g/10 min (190° C., load 2160 g)], and an adhesiveresin (high density polyethylene modified with maleic anhydride, ModicAP H521 manufactured by Mitsubishi Chemical Corporation) were suppliedto a multilayer extrusion device having a multilayer T die equipped withfeed block 3 kinds 5 layers and co-extruded at a processing temperatureof die temperature 250° C. to give a multilayer structure (multilayerfilm) of the present invention having a layer constitution (thickness40/5/20/5/40 μm) of polyethylene layer/adhesive resin layer/layer ofresin composition/adhesive resin layer/polyethylene layer.

The appearance, forming stability, adhesion between layers, resistanceto pinholes and oxygen barrier property of the obtained multilayer filmwere evaluated as shown below. The forming stability was also evaluatedwhen a multilayer structure was formed at a processing temperature ofdie temperature 220° C.

(Appearance)

The surface of a multilayer film was observed with a microscope, thenumber of foreign substances having a diameter of not less than 0.1 mm,which were present in the layer of the resin composition, was counted(per 10 cm×10 cm) and evaluated as follows.

-   -   ◯ . . . 0-1    -   Δ . . . 2-5    -   × . . . not less than 6        (Forming Stability)

The torque of the extruder after 1 hr and 10 hr from the start of theproduction of the above-mentioned multilayer film was examined for 10min and the stability (%) was calculated from the average value andevaluated as follows.Stability (%)={|torque after 10 hr−torque after 1 hr|/torque after 1hr}×100

-   -   ◯ . . . less than 10%    -   Δ . . . 10%—less than 15%    -   × . . . not less than 15%        (Adhesion Between Layers)

A multilayer film was cut into a rectangle of 1 cm in the MD directionand 10 cm in the TD direction, and the peel strength (g/cm) of theadhesive resin layer and the layer of resin composition was measured at23° C. in a 50% RH atmosphere by T peel method (tension speed of 100mm/min).

(Resistance to Pinholes)

The oxygen permeability [measured using OXTRAN2/20 manufactured by MOCONby an isobaric method (MOCON method) under conditions of 23° C., 80% RH]of a multilayer film after 500 times of bending by Gelbo flex tester wasmeasured, the ratio of oxygen permeability relative to the measurebefore bending (oxygen permeability after bending/oxygen permeabilitybefore bending) was calculated, and evaluated as follows.

-   -   ◯ . . . less than 1.2    -   Δ . . . 1.2—less than 2.0    -   × . . . not less than 2.0        (Oxygen Barrier Property)

The oxygen permeation of a multilayer film after irradiation of UV in anenergy amount of 1000 mJ/cm² at 23° C., 80% RH was measured according tothe above-mentioned method and the number of days until integratedoxygen permeation exceeded 5 cc per 1 m² was counted.

Example 2

In the same manner as in Example 1 except that the amount of9,10-anthraquinone-o-sodium sulfonate (B) added in the preparation ofthe resin composition (pellet) was 1.5% of EVOH (A), which was free ofwater, a multilayer structure (multilayer film) was produced andsubjected to the evaluation.

Example 3

In the same manner as in Example 1 except that 0.05 equivalent ofnicotinic acid was added as acid (C) relative to9,10-anthraquinone-β-sodium sulfonate (B) in the preparation of theresin composition (pellet), a multilayer structure (multilayer film) wasproduced and subjected to the evaluation.

Example 4

In the same manner as in Example 3 except that EVOH [ethylene content 44mol %, saponification degree 99.8 mol %, MFR 12 g/10 min (210° C., load:2160 g)] having a water content 30% was used as EVOH (A) in thepreparation of the resin composition (pellet), a multilayer structure(multilayer film) was produced and subjected to the evaluation.

Example 5

In the same manner as in Example 1 except that9,10-anthraquinone-2,6-di(sodium sulfonate) [percent weight loss byheating at 250° C. for 60 min of 0.1%] was used instead of9,10-anthraquinone-β-sodium sulfonate in the preparation of the resincomposition (pellet), a multilayer structure (multilayer film) wasproduced and subjected to the evaluation.

Example 6

In the same manner as in Example 1 except that EVOH (A) [ethylenecontent 32 mol %, saponification degree 99.5 mol %, MFR 12 g/10 min(210° C., load: 2160 g)] having a water content of 0.3% was used as EVOH(A) and melt-mixed at a melting temperature of 230° C. in thepreparation of the resin composition (pellet), a multilayer structure(multilayer film) was produced and subjected to the evaluation.

Comparative Example 1

In the same manner as in Example 1 except that9,10-anthraquinone-β-sodium sulfonate (B) was not added in thepreparation of the resin composition (pellet), a multilayer structure(multilayer film) was produced and subjected to the evaluation.

Comparative Example 2

When preparing a resin composition (pellet),2-t-butyl-9,10-anthraquinone (B) [percent weight loss by heating at 250°C. for 60 min of 95%] was used instead of 9,10-anthraquinone-β-sodiumsulfonate (B) and melt-kneaded with EVOH (A) having a water content of35%, but uniform melt-kneading was not achieved. Therefore, in the samemanner as in Example 1 except that 2-t-butyl-9,10-anthraquinone (B) wasmelt kneaded with EVOH (A) having a water content of 0.2% at a meltingtemperature of 230° C., a multilayer structure (multilayer film) wasproduced and subjected to the evaluation. The pellet had a water contentof 0.15%, and did not require drying.

Comparative Example 3

When preparing a resin composition (pellet), LDPE (Novatec LDLF660Hmanufactured by Japan Polychem Corporation) was used instead of EVOH (A)and melt-kneaded at a melting temperature of 95° C., but uniformmelt-kneading was not achieved. Therefore, in the same manner as inExample 1 except that the melt-kneading was performed at a meltingtemperature of 230° C., a multilayer structure (multilayer film) wasproduced and subjected to the evaluation.

Comparative Example 4

In the same manner as in Example 1 except that reduced iron was usedinstead of 9,10-anthraquinone-β-sodium sulfonate (B) in the preparationof the resin composition (pellet), a multilayer structure (multilayerfilm) was produced and subjected to the evaluation.

The evaluation results of Examples and Comparative Examples are shown inTable 1. TABLE 1 adhesion forming between resistance oxygen stabilitylayers to barrier appearance 220° C. 250° C. (g/cm) pinholes propertyEx. 1 ◯ ◯ Δ 350 ◯ 5 days Ex. 2 ◯ ◯ ◯ 320 Δ 3 days Ex. 3 ◯ ◯ ◯ 380 ◯ 5days Ex. 4 ◯ ◯ ◯ 320 ◯ 3 days Ex. 5 ◯ ◯ Δ 340 ◯ 5 days Ex. 6 Δ ◯ ◯ 300 ◯4 days Com. Ex. 1 ◯ ◯ ◯ 250 Δ 2 days Com. Ex. 2 ◯ ◯ X 230 Δ 6 days Com.Ex. 3 X X X 350 * * Com. Ex. 4 X Δ Δ 60 X 4 days*Evaluation was unavailable because oxygen permeability was large andexceeded measurable upper limit.

INDUSTRIAL APPLICABILITY

The resin composition of the present invention contains EVOH (A) andparticular anthraquinone (B). Therefore, when a multilayer structure isformed, the structure is superior in appearance, oxygen barrierproperty, further forming stability, resistance to pinholes, adhesionbetween layers and the like. A multilayer structure comprising the layerof resin composition as an intermediate layer is useful for packaging offoods such as meat, ketchup, soybean paste, beer and the like.

This application is based on a patent application No. 2002-182340 filedin Japan, the contents of which are hereby incorporated by reference.

1. A resin composition comprising a saponified ethylene-vinyl acetatecopolymer (A) and a substituted; 9,1 0-anthraquinone (B) having asubstituent at at least one of the 2-, 3-, 6- and 7-positions andshowing a percent weight loss when stood with heating at 250° C. for 60minutes of not more than 5%.
 2. The resin composition of claim 1,wherein the substituted 9,10-anthraquinone (B) having a substituent atat least one of the 2-, 3-, 6- and 7-positions and showing a percentweight loss when stood with heating at 250° C. for 60 minutes of notmore than 5% is water-soluble.
 3. The resin composition of claim 2,wherein substituted 9,10-anthraquinone (B) having a substituent at atleast one of the 2-, 3-, 6- and 7-positions and showing a percent weightloss when stood with heating at 250° C. for 60 minutes of not more than5% is sodium anthraquinone-sulfonate or disodiumanthraquinone-disulfonate.
 4. The resin composition of claim 1, whereinthe content of the substituted 9,10-anthraquinone (B) having asubstituent at at least one of the 2-, 3-, 6- and, 7-positions andshowing a percent weight loss when stood with heating at 250° C. for 60minutes of not more than 5% is 0.5-10 wt % relative to the saponifiedethylene-vinyl acetate copolymer (A).
 5. The resin composition of claim1, further comprising an acid (C) in 0.001-0.5 equivalent of thesubstituted 9,10-anthraquinone (B) having a substituent at at least oneof the 2-, 3-, 6- and 7-positions and showing a percent weight loss whenstood with heating at 250° C. for 60 minutes of not more than 5%.
 6. Theresin composition of claim 1, which is obtained by melt-mixing asaponified ethylene-vinyl acetate copolymer (A) having a water contentof not more than 60 wt % and a substituted 9,10-anthraquinone (B) havinga substituent at at least one of the 2-, 3-, 6- and 7-positions andshowing a percent weight loss when stood with heating at 250° C. for 60minutes of not more than 5% in an extruder.
 7. A laminate structurecomprising a layer made of the resin composition of claim 1 as anintermediate layer, and at least one layer of inner and outer layerscomprises a resin selected from a polyolefin resin, a polyamide resinand a polyester resin.
 8. The laminate structure of claim 7, wherein theinner and outer layers comprises a polyolefin resin.
 9. The resincomposition of claim 6, wherein the saponified ethylene-vinyl acetatecopolymer (A) has a water-content of 20-60 wt %.